The present invention relates to powdery compounds of the formulation NiaMbOx(OH)y, a procedure to produce the same, and the use of the same as active material for nickel metal hydride batteries and/or as precursor for the production of lithium compounds for use in secondary lithium batteries.
JP10027611 A discloses the synthesis of a co-precipitated mixed hydroxide containing at least the two metals nickel and cobalt, but which is not limited to the aforementioned. The co-precipitated mixed hydroxide is processed further to lithium mixed metal oxides as active mass for secondary lithium batteries. The co-precipitation of the elements on the level of the precursor allows for producing lithium mixed metal oxide that will result in the electro-chemical cycle behaviour improving if the same is used in secondary lithium batteries. In this, the molar nickel share in the lithium mixed metal oxides, referring to the metal elements except for lithium, is at least 70%.
In US 2002/0053663 A1 a co-precipitated nickel cobalt manganese hydroxide is claimed that is characterised by a tap density of at least 1.5 g/cm3. The co-precipitated mixed hydroxide serves as precursor for the synthesis of lithium nickel cobalt manganese oxides (LNCMO). Using processes described as “conventional” within the framework of the patent, no mixed hydroxide with a high tap density may be produced. The high tap density of the mixed hydroxide is of such high importance, because it has a positive effect on the tap density of the end product, which in turn influences the volumetric energy density in a secondary lithium battery. Within the framework of the examples powders are disclosed, the tap densities of which are between 1.71 and 1.91 g/cm3. In this, the average particle size of the powders is 5-20 μm. In US 2002/0053663 A1 mixed hydroxides with high tap densities were obtained by implementing the precipitation either at inert or even at reduced conditions.
US 2003/0054251 A1 describes an optimised procedure for the synthesis of nickel- and manganese-containing mixed oxides respectively mixed hydroxides as precursors for the cathodic active mass in secondary lithium batteries. The main idea of this invention is to subject the co-precipitated mixed hydroxides (e.g. of the metals Ni, Co, Mn) already mentioned within the framework of the literature to a thermal pre-treatment at 300-500° C. before the actual oven process, in order to obtain a so-called “dry precursor”. Afterwards, this dry precursor is equipped with a lithium component and converted into LNCMO by an annealing procedure. If the described, dried precursor is used instead of a (non-dried) mixed hydroxide, an end product will be obtained in accordance with this document that is characterised by an increased product consistency when compared to materials, which the non-dried mixed hydroxide is used for. The product consistency of the material has been determined by producing twenty batteries in each case with each material and by evaluating the variation of the loss of capacity between the third and the three hundredth electro-chemical cycle for these twenty batteries.
On the basis of WO003004418 it is known that the typical grain size of spherical nickel hydroxides for the use in nickel metal hydride batteries (hereafter abbreviated with NiMH) is between 5 and 15 μm. The importance of the tap density of nickel hydroxide as regards to achieving high energy densities in NiMH batteries is also described within the framework of WO003004418. A correlation between tap density and particle size is also described at this point. With its content the document JP-10-097856 aims at producing nickel hydroxides that are as dense as possible, at which the same are to be used as active material of the positive electrode of NiMH batteries. Furthermore, the nickel hydroxide is also to be characterised by a high degree of utilisation, as well as a good cycle resistance at high temperatures. The dense nickel hydroxide with tap densities of at least 2.0 g/cm3 was obtained by adjusting the average particle size to a value between 5 and 20 μm, amongst others.
Within the framework of their work, Fierro et. al., J. Electrochem. Soc 153 (3) (2006), page A492-A496 also describe differently doped nickel hydroxides designed to be used as active material for NiMH batteries. For the nickel hydroxides described therein, the tap densities are above a value of 2.0 g/cm3 as well, namely between 2.15 and 2.20 g/cm3. Here, average grain sizes in the range of 8.3 to 12.0 μm are required to achieve such high levels of tap densities.
The nickel mixed metal hydroxides produced in accordance with the quoted state-of-the-art are used for both as raw material for the production of cathode materials for secondary lithium batteries and directly as active mass for NiMH batteries. Such secondary batteries are suitable for being used in hybrid and electric vehicles to a limited extent only. Being able to unload and load the batteries is required for both types of vehicles in order to be able to achieve high levels of acceleration and to re-convert the kinetic energy of the vehicle to electrical energy with the least possible thermal losses when decelerating the vehicle. In case of specified energy for a certain acceleration or deceleration procedure, the required loading/unloading rate, expressed in ±Δ overall capacity/Δt, is lower the higher the overall capacity of the battery. Thus, achieving a volume capacity of the battery that is as high as possible is aimed at not only on the basis of space and cost reasons, but also on the basis of electrical reasons. Furthermore, as regards to the pure electric vehicle the aforementioned as absolutely necessary, because the capacity naturally determines the action radius and the same is absolutely decisive for the marketability of these vehicles.